Electrically heated base for cooking



May 12, 1953 R. N. KIRCHER Erm. 2,638,526

ELECTRICALLY HEATED BASE FOR COOKING 2 snee's-sheet 1 Filed 001;. 13,1950 Flc-,5'

AAT-royaum# Sab May l2, 1953 R. N. KlRcHER Erm. l 2,638,526

' ELECTRICALLY HEATED BASE FOR COOKING Filed Oct. 13, 1950 2Sheets-Sheet 2 INVENToRs RALPH N. Km0-ea BY Wmumvx G. LAABS o. Mul

Patented May 12, `1953 ELECTRICALLY HEATED BASE FOR 'COOKING Ralph N.Kircher and William G. Laabs, West Bend, Wis., assignors to West BendAluminum Co., West Bend, Wis., a corporation of Wisconsin ApplicationOctober 13, 1950, Serial No. 189,938

This invention relates to improvements in electrically heated bases forcooking utensils, and particularly for such bases adapted to be used forsmall portable ovens or the like.

Portable ovens have been designed for use on the open tops of gas orelectric stoves. In some quarters stoves are not available and it isdesirable to have an electrically heated base for such ovens or othercooking utensils. `Such bases to be practical must be capable of beingpositioned directly on a table or counter top or the like and usedWithout damaging such topsby'heat.

OneV of the objects of this invention, therefore, is to provide such anelectrically heated base which in operation will not vtransmit andradiate downwardly enough heat to damage table tops.

Another object of this invention is to provide an electrically heatedbase which is thermostatically controlled by the temperature within theoven or other cooking utensil heated thereby without interfering withthe removal of the oven top or interchange of cooking utensils.

A` still further object of this invention is to provide an electricallyheated base of the kind herein described which is comparativelyinexpensive to produce and assemble.

.In the attainment of these objects certain features are important. Theheating element is mounted below a work-receiving top and above theperipheral margin of a reflector. The re- :flector is made of aluminumbecausesuch metal does not lose its reflecting qualities with prolongeduse. The central portion of the reector is convex upwardly to direct therays of heat toward the perimeter of the top. The reflector and top arecarried on a body spaced substantially from the bottom thereof. Thesides of the body immediately below the reflector are slotted to provideupper ventilators. The bottom, which acts as a protector reflector, isalso provided with Ventilating openings. Thus most of the heat generatedby the heating element is radiated or transmitted to the top. Any heatradiating downwardly from the reflector will be reflected upwardly bythe bottom and not transmitted therethrough to the table top. The airbetween the bottom and the reflector which becomes heated will rise andescape through the upper ventilators and be replaced by cool airentering upwardly through the Ventilating openings in the bottom. `Ofcourse the bottom will become heated somewhat above ambient temperaturebut it is provided with feet of heat-resistant material and spaced areasonable.A dis- 6 Claims. (Cl. 21S- 19) tance from the table top orother surface on which the base is positioned. Thus there is no directcontact and the amount of heat radiated downwardly from the bottom isnot suflicient to do any damage to such top or surface.

VControl of the unit is obtained by using two sections of heatingelements connected in parallel with a thermostatic switch to disconnectone of the sections. The thermostatic switch is preferably positionedbetween the reiiector and the bottom and adjacent an opening in thecentral portion of the reflector. Thusly positioned the thermostaticswitch willbe operated to open the circuit to one of the heating elementsections when the air between the reector and the bottom reachesapredetermined degree. This will cut substantially in half the amount ofheat being generated so that losses will be in excess of input andtemperatures will drop. However, if there is a sudden drop intemperature due to the condensation of steam passing down through theopening in the reflector, such condensation will be directly applied tothe thermostat and cause it to rapidly close the switch again increasingthe heat input.

The novel features which are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its organiza-V tion and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of a specificembodiment when read in connection with the accompanying drawings inwhich: 4

Fig. 1 is a view in side elevation of` an electrically heated baseembodying the present invention with parts broken away and shown insection for the sake of clarity in illustration;

Fig. 2 is a top plan view of such base;

Fig. 3 is a bottom plan view of such base;

Fig. 4 is anv enlarged fragmentary sectional View taken on line 4 4 ofFig. 3;

Fig. 5 is a fragmentary schematic view showing the shape of the bottomas blanked or cut from the body in the manufacture of such base;

Fig. 6 is an enlarged fragmentary sectional View taken on line 6 6 ofFig. 2;

Fig. I is an enlarged fragmentary sectional View taken on line 'l-'I ofFig. 2; and

Fig. 8 is a schematic wiring diagram illustrating the electricalconnections of the heating elements and thermostatically controlledswitch.

As is seen Afrom the drawings, the essential elements of theelectrically heated base comprise a bottom It, a body 22 supported onthe bottom, a reector 42 mounted on the top of the body and spaced fromthe bottom, heating elements 5t above and carried by such reflector, athermostatic switch 64 for controlling the heating elements between suchreflector and. bottom, and a top itV which comprises the bottom of theoven. on which the over top (not shown) is seated or on which othercooking utensils are placed.

These elements are held together by a single bolt 16 which extends fromthe top 'Mt tol the bottom Il).

The bottom le is cut or blanked from the same sheet of material as the.7body 22 in accordance with the layout shown. iri. Fig. 5. As. a resultthe perimeter oi the bottom Ii) has a plurality of notches l2 spaced byintervening projections I4 and the inner edge of' the body 22 hascomplementary projections 28 and intervening notches 2S. In thisexemplication the projections.- i4 are. angularly longer than thenotches l2v to. provide turned-up locating lugsI 2tt (see Fig. fi)which.. engage the projections 28 when the body is assembled on thebottom to prevent relative rotation therebetween. It is. also desirableto` have radially extending upwardly projecting ribs it formed on theprojections M to space. such projections. from the projections 28 and.thereby lessen. the amount. ci heat that will be. conducted from thebody 22 to the bot.- tom i0-, The locating lugs and spacing ribs may beformed on theaprojectons 28. instead ot the. projections i4 andaccomplish the same function. Mechanically it is a little simpler toform such. elements on the projections i4 because the dies. andlshaping. steps. or the bottom lil are much more. simple than. in, the.case oi. the. body. The. bottom til is supported above the surface. ofthe table or counter on. which itl rests by three substantially equallyangularly spaced legs t8 made of. heat-insulating material and fastenedto. the bottom in the usual'v manner. Howeven, it is desirable to.locate the feet i8 so that each one is in alinement with a notch I2 andare thus directly in the path. of air moving up through the Ventilatingopenings formed by the cooperation of notches I2 and 26.

The body 2.2, has a lower inturned flange 24 on the inner edge of whichare the. notches 2t and projections 2e heretofore described inconnection with the bottom l0. The side oi the body 22,. adjacent theupper end, has a plurality' of radially spaced Ventilating slots 30. tolet heated air now from between the bottom` ti! and reflector 42. Thetop edge of' the body 22 has an annular shoulder terminating in an uppervertical ange 32. This flange, as is shown in Fig. 7, may be notched' atspaced portions' to provide inwardlyv bent tabs 34 on which thereflector 42 can be supported. However, the reector 42 can rest directlyon the top of flange 32. There can be a notch 36 in such flange whichwill receive a tongue 3T ron the reector 42 to angularly relativelylocate such members. Such location maybe accomplished however by anassembly jig and the parts thereafter held against rotation by'frictional' fit'. Electrical plug type terminals 38a and 38h of standardconstruction are insulatingly secured in the customary mannerinopeningsI in the side of' the body 22 with4 their exterior portionsadaptedl for' tting into an electrical socket and their interior portionconnected to the heating elements. To facilitate the handling of theelectrical base the body 22" has secured at opposite sides thereofhandles te made of heat-insulatix-ig material.

' temperature above ambient temperature.

The body 22 is assembled on the bottom IIJ by relatively angularlylocating the projections 28 so that they seat upon the projections I4.This brings the notches I2 opposite the notches 2S to form Ventilatingopenings in the bottom of the: base through. which air may ascend asheated air within the. body 22 escapes out through the slots 3G. Theimportance of this arrangement is that it not only provides for coolingby means of convection of air but also breaks up the sectionaicontinuity of the metal between body and bottom greatly lessening thetransfer of heat by conduction to the` bottom.

The. reiiect'or 42S. is formed from sheet aluminum because retains itsreflecting quality with continued use, and the central portion thereofis arched upwardly in semi-dome fashion, as is shown in Fig. 1', toradiate heat toward the perimeter thereof. A plurality oi slots 46 arecut in the peripheral margin of the reflector 42 'and spaced in twocircularly extending rows.

The material cut. from these slots is bent. downwardly to form holdinglugs 48... Ceramic insulators 44 are inserted upwardly through. theslots. 45 and the. lugs 48 are. bent up against. the wider basey of theinsulators4 to lock such in.- sulators in place within the. slotssubstantially in the manner shown in. Fig.. 6. The heating elementconsists of. an outer section Ema andv an inner section 5th held` by theinherent spring action thereof in the insulators 44., This constructionlocates. the heating. elementv closely adjacentI the perimeter of theredector which is desirable in the. case of portable ovens as will bemore. fully pointed out Inwardly of. the heating, elements the reflector42. is provided with a rectangularly shaped opening 54' having inwardprojections. 56. An insulating terminal block 52 is. inserted thisopening from the bottom o' the reiector with an enlarged base restingagainst the lower surface of the reector. The projections. 5.6 are bentagainst such base to hold the block in place. Three threaded'. terminals58a, 586,. and. 58.0. are mounted in the terminal block 52 and providethe means of electrically connecting the heatingl element, sections tothe plugs 38a and 33h and the thermostatically operated switch 64 in themanner hereinafter described. In using the electrically heated base forheating a portable oVen steam is' often generated within the oven and toprovide for its escape the reiiector 42 has a centrally located opening5U. To simplify manufacturing proc'- esses, theA material cut from therefiector 4'2 to form such opening is bent. downwardly to provide a.mounting 62 which supports the thermostatic switch indicated generallyat 64.

The thermostatically controlled switch 64, which is secured to the.mounting S2' by a bolt and nut. 6E, is of standard design and does notform a part of this invention and is not described in detail. It isessential that the switch be normally biased to closed4 position andthat its contacts open when its bimetal-lic power element. is subjectedto a predetermined degree ofv Like standard switches' of this type theunit has a factory adjustment to regulate it to operate at the desiredtemperature. Ribbon-like conductors et electrically connect one of thecontacts of' the switch iid to the terminal 5ta', the other of theswitch contacts 'to the terminal 58h, the terminal 58h to the plug 38u,and the terminal 58e tothe plu-g' 38h. One end of each of heating ele-`ment sectionsv 50c. and 50i?1 is electrically connested to the terminal56e'. The other end of section 50a is connected to terminal 58h and theother end of heating section 50h is connected to terminal 58a. As isshown in the schematic diagram of Fig. 8, the switch 64 is normallyclosed tov` connect the sections 50a and 50h in parallel across thesource of electrical power. When the heat rises in the body 22 to thepredetermined degree, the thermostatic switch 64 will open and thesection 50h will be disconnected. Thereafter heat will be generated onlyby the section 50a.

The top l0, which also constitutes the bottom of the portable oven, ismade of stainless steel because its surface darkens with use and thismakes the top more heat-absorbing. The top i0 has a depending flange 14which snugly fits around the vertical flange 32 and supports the One ofthe features of this invention resides 0 in the relative positioning ofthese openings with respect to the heating element. As is shown in Fig.2 the section 50a is in substantially vertical alinement with theopenings 12. This permits direct radiation of heat from the heatingelement through the openings 'l2 to the oven cover (not shown).

Another feature of this invention is the positioning of the thermostaticswitch 64 between the reflector 42 and the bottom I0, closer to thebottom than to the reilector. Thus positioned the thermostat will beoperated to cut down the heat supply before enough heat can be absorbedby the bottom I0 to cause it to radiate a dangerous amount downwardlytoward the table top or other supporting surface. In addition to thisthe thermostat is located in substantial alinement with the opening 60.Thus as steam is generated in the oven and is forced downwardly throughthe openings 'l2 and opening 6i), such steam will directly strikeagainst the thermostat switch 64. The cooling effect of the steam as itcondenses will cause the thermostat switch, if the switch is then open,to rapidly close and thus supply additional heat in anticipation of thecooling action taking place within the oven by condensation of suchsteam therein.

Although only one embodiment of the invention is shown and describedherein, it will be understood that this application is intended to coversuch changes or modifications as come within the spirit of the inventionor scope of the following claims:

We claim:

1.1n an electrically heated base for small portable ovens or the like, abottom provided with means for supporting said bottom spaced from atable top or the like, a body having upper and lower ends mounted onsaid bottom with said lower end in engagement with said bottom, saidbottom being formed from the same piece of material as said body andhaving an outer periphery with notches and projections, said lower endof said body having an opening with notches and projections adapted tointert with notches and projections on said bottom, said body and bottombeing positioned with the projections on said body resting on theprojections on said bottom` to support said body, said notches on each`being in alinement to provide ventilating openings, a reflector mountedon said upper end, a heating element supported by and above saidreflector, and a top carried by said body and extending over saidreflector and said heating element to provide a bottom for a portableoven or the like.

2. In an electrically heated base for small portable ovens or the like,a bottom provided with means for supporting said bottom spaced from atable top or the like, a body having upper and lower ends mounted onsaid bottom with said lower end in engagement with said bottom, saidbottom being formed from the same piece of material as said body andhaving an outer periphery with notches and projections, said lower endof said body having an opening with notches and projections adapted tointert with notches and projections on said bottom, said body and bottombeing positioned with the projections on said body resting on theprojections on said bottom to support said body, said notches on eachbeing in alinement to provide Ventilating openings, a reector mounted onsaid upper end, said body having vents near said upper end below saidreilector to permit fluids to move by convection upwardly through saidbody from said Ventilating openings, a heating element supported by andabove said reflector, and a top carried by said body and extending oversaid reector and said heating element to provide a bottom for a portableoven or the like.

3. In an electrically heated base for small portable ovens or the like,a bottom having on its perimeter radial projections spaced by notches, abody having a lower inturned ange terminating in an inner edge, saidedge having radial projections spaced by notches, said body beingpositioned on said bottom with the projections of said body resting onthe projections of said bottom and with the notches of said bodyopposite the notches of said bottom to form Ventilating openings, theedges of one of the projections of one said bottom or body being bent toform lugs engaging the projections on the other of said bottom or bodyto prevent rotational displacement therebetween, an electric heatingelement carried by said body, and means for holding said bottom and bodyassembled.

4. In an electrically heated base for small portable ovens or the like,a bottom provided with means for supporting said bottom spaced from atable top or the like, a body mounted on said bottom and having upperand lower ends with said lower end in engagement with said bottom, saidupper end terminating in a vertical peripheral flange, a relatively thinaluminum reflector having an outer edge extending to and supported bysaid vertical peripheral flange, said reector having a peripheral margintherearound adjacent to said outer edge, a heating element carried byinsulators on said reflector and positioned above and in substantialvertical alinement with said peripheral margin and closely adjacent saidouter edge, said reiiector being arched upwardly in semi-dome fashionfrom the inner edge of said peripheral margin to the center of saidreflector to provide a curved surface for radiating heat from saidheating element toward the outer edge or said reflector, and a topcarried by said body and extending over said reflector and said heatingelement to provide a bottom for a portable oven. or the like.

